The invention relates to a method and a device for fitting a rotary throttling unit in the passage defined by a pipe, said unit comprising a shaft which passes through the pipe and a butterfly valve having a shape corresponding to that of the pipe, inserted in a radial slit of the shaft and fastened thereto, for example by squeezing the slit.
The invention is particularly, although not exclusively, applicable to the fitting of a rotary airflow throttling unit in a butterfly valve body for adjusting the airflow in injection feed systems for internal combustion engines and in carburettors.
Assembling methods are already known including the steps of inserting the shaft accross the pipe and providing it with elements which define its axial free movement; the butterfly valve is then introduced into the slit and the shaft is brought into the angular position in which the butterfly valve closes the passage of the pipe before the butterfly valve is secured to the shaft. A method for carrying out these operations automatically is described in French patent publication No. 2 642 498.
The slit has an axial length slightly greater than the width of the butterfly valve, so that the shaft may be adjusted axially with respect to the butterfly valve. When the latter is in closed position, it is fixed with respect to the pipe. The shaft may then be moved between a first and a second stop position defined by abutment of the elements which it carries. To reduce the friction, none of these elements must bear on the pipe during normal operation. To obtain this result, while the amount of free movement between the two abutting positions is generally only a few tenths of a mm, attempt is made to balance the clearances which exist between the pipe and the elements coming into abutment before the butterfly valve is secured to the shaft. At the present time, this operation is carried out by assessing the clearances visually. This method is difficult and does not allow the desired degree of reliability and accuracy to be obtained.